Try the Motley Fool share dealing service. They have flat fees for both UK and International trades.

Go to a discount broker.

The cheapest dealers | Money | The Guardian

Can't advise re facebook shares but don't buy more than you can comfortably afford to loose.

I use Barclays, no idea if its the "best", but it came free with the premier account many moons ago.

As to facebook as an investment? IMHO they are making a mistake by mandating the Timeline interface before the IPO. Losing 10-15% users might dent the valuation significantly.

And no matter how many times this happens, look at the basics. Facebook is valued at $100billion. Based on what? Not revenues, and not book worth, but 'hysteria'. Think Global Crossing circa 2000, Worldcomm 2001.

I think the IPO itself could torpedo Facebook. The firm has already lost its aura of "cool", and its long-delayed income stream - upon which the IPO is valued - comes from the very same advertising that is starting to hack off many users who naively subscribed to the original free/cool/yoof aspects. I reckon it will only take a data privacy scandal, or a fresh new fad, and FB will completely implode....

For me I worry about the leadership. Either he's running a company or a social experiment, or more likely he can't make his mind up. For me it's the clincher, it's a high-risk stock pretending its a big corporate. No sale.

Originally Posted by Victorian_Major

For me I worry about the leadership. Either he's running a company or a social experiment, or more likely he can't make his mind up. For me it's the clincher, it's a high-risk stock pretending its a big corporate. No sale.

I'd agree. With my modest dabblings I prefer a CEO to be a hard nosed bastard interested in making money rather that trying to teach the world to sing in perfect harmony. Not sure Zukerbergs letter to potential investors will help?

Facebook was not originally created to be a company. It was built to accomplish a social mission — to make the world more open and connected.

Building great things means taking risks. This can be scary and prevents most companies from doing the bold things they should. However, in a world that’s changing so quickly, you’re guaranteed to fail if you don’t take any risks. We have another saying: “The riskiest thing is to take no risks.” We encourage everyone to make bold decisions, even if that means being wrong some of the time.

Full transcript...

Mark Zuckerberg's Letter to Investors: 'The Hacker Way' | Epicenter | Wired.com

I'd suggest having a good read here

Facebook IPO: Boom or bubble? • The Register

But, who knows?